Since diamond has high hardness and a wide band gap, the application of diamond is being tested as a coating material for a device, a light transmitting material, a high frequency semiconductor, an electronic device capable of operating at high temperature, or the like. As a method of artificially forming diamond, the CVD method applicable to various substrate materials is mainly used. In the CVD method source, gas including carbon atoms is dissociated and reacted at low pressure, thus forming a diamond film on a substrate surface. Generally known CVD diamond films are in a polycrystalline state, and have unevenness on the growth surface. Thus, in order to apply a CVD polycrystalline diamond film formed on a large area of a substrate to various purposes, the diamond film should be smoothed. In addition to the smoothing of a diamond surface, an etching technique of to form preferable patterns is also required.
Conventional smoothing methods of a diamond surface are a mechanical polishing treatment, the method of etching the surface with laser irradiation in an oxygen atmosphere, a reactive ion etching (RIE) method with etching gas such as argon and oxygen, a physical etching with single ion irradiation ("Diamond No Ion Beam Kako" (Ion Beam Smoothing of Diamonds), New Diamond, Vol.5, No.1, 18-25(1989)), and the like.
However, generally speaking, diamonds are extremely hard and stable chemically, so that it is difficult to smooth diamonds by conventional mechanical polishing treatments and etching methods. Moreover, in the conventional methods, the processing efficiency and the precision are poor.